During normal anesthesia, and particularly when muscle relaxants are utilized, a nerve or muscle stimulator is utilized to impose a muscle twitch as a means of determining the current effectiveness of the medication on the patient. Such nerve or muscle stimulators are variously called "muscle relaxant indicators" or "nerve stimulators" or "nerve locators" and are commonly available and include generator units that produce timed electrical pulses that can be used to stimulate a nerve or a muscle. Various such devices utilize both audible and visual indicators for the electric pulse. A typical nerve stimulator is the Norcuron.RTM. peripheral nerve stimulator, manufactured for Organon Inc., West Orange, N.J. 07052 by Neuro Technology of Houston, TX. However, in current devices both the audible and visual indicators are located at the generator unit. The generator unit may be a hand-held battery powered unit wherein the anesthesiologist's attention is directed to the activated end of the muscle.
The muscle, when energized by the pulse, will, unless completely sedated, twitch. The anesthesiologist is therefore focusing on the appropriate anatomical location for indications of twitch. Because it is desired to detect the early onset of muscle movement, the actual twitch may be quite faint. That is, the movement may be very small. In order to distinguish from non-stimulated movements that might occur, it is necessary for the anesthesiologist to detect the pulse induced movements only. To do this the anesthesiologist must correlate the timing of the induced pulse, to the actual movement that occurs either by listening for the audible indicator or by watching the visual indicator. Because the buzzer is very faint, it frequently cannot be heard in the operating room. Making a louder buzzer may not be practical in an operating room where the repeated triggering of the pulse would disrupt communication and provide an annoying background. It is also very complex to watch both the visual indicator at the generator unit and the anatomical spot under observation.